A conventional soft magnetic material applicable to a core of a magnetic head, a transformer, a motor, etc., includes a Fe—Si alloy, a Fe—Si—Al alloy (Sendust), a Ni—Fe alloy (Permalloy), and a Fe-based or Co-based amorphous alloy material. When a soft magnetic material is applied to a DC motor core etc., it is generally effective to form the soft magnetic material in a high-density bulk shape. Contrary to this need, the conventional amorphous alloy material prepared by quenching molten metal has been able to be formed only in a limited shape, such as thin strip, wire, powder or thin film.
In the circumstances, a method comprising mechanically crushing the amorphous alloy thin strip, sintering the obtained alloy powder, and solidifying/forming the sintered alloy in a bulk shape has been developed. However, this method has a problem about difficulties in obtaining a high-density sintered body due to the need for performing the sintering process at a relatively low temperature to prevent the alloy powder from being crystallized during the sintering process.
The dream of forming an amorphous alloy in a bulk shape has been realized by a “metallic glass alloy”. Specifically, in the 1980s, an alloy having a high glass forming ability was found in Pd—Si—Cu alloys. Further, since 1990, alloys having an extremely high glass forming ability were found. Generally, in an “amorphous alloy”, crystallization is developed during heating before reaching a glass transition point, and no glass transition can be observed on an experimental basis. In contrast, in the “metallic glass alloy”, a clear glass transition is observed during heating, and a temperature interval of a supercooled liquid region before a crystallization temperature increases up to several ten K. This property has opened the way for forming a bulk amorphous alloy by a casting method using a cupper die with a low cooling rate. The reason why such an amorphous alloy is particularly called “metallic glass” is that it is a stable amorphous material like an oxide glass, and subject to plastic deformation (viscous flow) at a high temperature, even though it is metal.
The “metallic glass alloy” has a high glass forming ability, or a characteristic capable of being solidified from the molten alloy in a supercooled liquid state though a casting process using a copper die or the like to produce a metal cast body consisting of a glass phase and having a larger size, the so-called “bulk shape”. The “metallic glass alloy” also has a characteristic capable of being heated to a supercooled liquid state and subjected to a plastic working. Essentially differently from the “amorphous alloy”, such as conventional amorphous thin strip or fiber, devoid of these characteristics, the “metallic glass alloy” has significantly high usefulness.
The inventors previously developed a Fe-based [Fe—Al—Ga—P—C—B based, Fe—(Co, Ni)—(Nb, Zr, Mo, Cr, V, W, Ta, Hf, Ti)—Ga—P—C—B based or Fe—(Co, Ni)—Ga—(P, C, B) based] soft magnetic metallic glass alloy containing Ga as an essential element (see the following Patent Publications 1 to 5). Further, a Fe-based [Fe—Al—P—C—B—(Cr, Mo, V) based] soft magnetic metallic glass alloy containing no Ga was developed (see the following Patent Publication 6).
Recently, a metallic glass sintered body prepared by sintering a metallic glass alloy powder having a supercooled liquid region has been proposed. This metallic glass sintered body is a bulk sintered body having no restraint in shape, and thereby can be suitably used in a core of a magnetic head, a transformer or a motor (see the following Patent Publications 7 to 10).
The inventors previously filed a patent application covering an invention on a Fe-based soft magnetic metallic glass sintered body prepared by spark-sintering particles having a primary component of a Fe-based [Fe—(Ti, Zr, Hf, V, Nb, Ta, Mo, W)—B based, Fe—Al—Ga—P—C—B—Si based, Fe—Co—Ni—(Zr, Nb)—B based, etc.] amorphous alloy, and a method for its production through a spark plasma sintering process (see the following Patent Publications 11 to 13). The inventors also filed a patent application covering an invention on a Fe-based soft magnetic metallic glass sintered body prepared by sintering plate-shaped particles of Fe-based (Fe—Al—Ga—P—C—B—Si based, etc.) amorphous alloy in a temperature range of 693 to 713 K (see the following Patent Publication 14). Further, the inventors reported a Fe-based soft magnetic metallic glass sintered body prepared by spark-discharging particles obtained through a gas atomizing process, which have a particle size of 10 to 30 μm, and a primary component of Fe—Co—Ga—P—C—B based amorphous alloy (see the following Non-Patent Publications 1 to 3).
Patent Publication 1: Japanese Patent Laid-Open Publication No. 08-333660
Patent Publication 2: Japanese Patent Laid-Open Publication No. 09-320827
Patent Publication 3: Japanese Patent Laid-Open Publication No. 11-071647
Patent Publication 4: Japanese Patent Laid-Open Publication No. 2001-152301
Patent Publication 5: Japanese Patent Laid-Open Publication No. 2001-316782
Patent Publication 6: Japanese Patent Laid-Open Publication No. 2002-226956
Patent Publication 7: Japanese Patent Laid-Open Publication No. 11-073608
Patent Publication 8: Japanese Patent Laid-Open Publication No. 11-073609
Patent Publication 9: Japanese Patent Laid-Open Publication No. 11-074109
Patent Publication 10: Japanese Patent Laid-Open Publication No. 11-074111
Patent Publication 11: Japanese Patent Laid-Open Publication No. 08-337839
Patent Publication 12: Japanese Patent Laid-Open Publication No. 10-092619
Patent Publication 13: Japanese Patent Laid-Open Publication No. 11-071648
Patent Publication 14: Japanese Patent Laid-Open Publication No. 2000-345308
Non-Patent Publication 1: Baolong Shen et al., “Bulk Formation by Spark-Plasma Sintering of Fe—Co—Ga—P—C—B Glass Alloy Powder and Magnetic Characteristics thereof”, Powder and Powder Metallurgy, Vol. 48, No. 9, September 2001, pp. 858-862
Non-Patent Publication 2: Baolong Shen et al., “Preparation of Fe65Co10Ga5P12C4B4 Glassy Alloy with Good Soft Magnetic Properties by Spark-Plasma Sintering of Glassy Power”, Materials Transactions, Vol. 43, No. 8, p. 1961-1965 (2002)
Non-Patent Publication 2: Baolong Shen et al., “Preparation of Fe65Co10Ga5P12C4B4 Metallic Glass Magnetic Core by Spark-Plasma Sintering”, “Journal of Japan Society of Powder and Powder Metallurgy”, November 2002, p. 196